Obsidian
Obsidian (Volcanic Glass) · Collector Mineral / Semi-Precious Gemstone
Crystal System
Amorphous (Non-crystalline); Typically occurs as massive or rounded nodules (Apache tears)
Mineral Group
Silicates (Natural Glass)
Chemical Formula
SiO2 (70–75%), with MgO, Fe3O4, and Al2O3
Formation Process
Igneous: Forms when felsic lava extruded from a volcano cools rapidly with minimum crystal growth
About This Crystal
A jet black, opaque to translucent natural glass with a vitreous (glassy) luster. Shows smooth, curved surfaces upon breaking and may contain minute bubbles or mineral inclusions (phenocrysts).
Physical Characteristics
Color: Black; Streak: White; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.35–2.60; Tenacity: Brittle; Fluorescence: Generally inert.
Optical Properties
Refractive Index: 1.48–1.51; Birefringence: None (isotropic); Pleochroism: None; Optical Phenomena: Sometimes exhibits gold or silver sheen due to gas bubbles.
Hardness & Durability
Origin Region
Volcanic regions including USA (Oregon, California), Iceland, Mexico, and Italy (Lipari)
Hardness & Durability
Mohs Hardness: 5.0–5.5; Toughness: Poor (fragile due to brittleness); Reliability: Sensitive to heat and mechanical shock.
Care & Maintenance
Clean with warm soapy water and a soft cloth; keep away from harder stones (like quartz or sapphire) to prevent scratching; avoid ultrasonic cleaners.
Rarity & Value
Common; Value is generally low ($1–$20 for rough), though 'Fire' or 'Rainbow' varieties command higher prices ($50+). No common treatments.
Special Characteristics
Strong conchoidal fracture produces extremely sharp edges; may show 'sheen' if bubbles are oriented; 'snowflake' pattern if partly devitrified.
Lore & History
Used by ancient civilizations for surgical blades, arrowheads, and mirrors. Historically associated with protection and grounding in folkloric traditions.